This is an expository review of the Lorentz transformation, which is a
change of coordinates used by one ''inertial observer'' to those used
by another one. The transformation can be represented by a four-by-fo
ur matrix, the Lorentz matrix or the Minkowski-Lorentz matrix. The mos
t familiar, or ''special,'' case has the x axis of both observers para
llel to their relative velocity. A more general transformation drops t
his constraint. But then a seeming ''paradox'' arises when there are t
hree observers, and this has led to a challenge to the self-consistenc
y of the special theory of relativity. It is shown here that this chal
lenge is based on a misunderstanding. The properties of the more gener
al Lorentz transformation are reviewed consistently in terms of the ma
trix approach, which the author believes is now the easiest approach t
o understand. The spectral analysis of the Lorentz matrix is also disc
ussed. Several checks are included to ''make assurance double sure.''